Multilayer ceramic electronic components and method for manufacturing the same

ABSTRACT

A multilayer ceramic electronic component includes a skittered laminated body including internal electrodes that have a strength that is greater than that of ceramic layers provided therein. End portions of the internal electrodes protrude from end surfaces of the laminated body and are deformed so as to extend along the end surfaces by a barrel polishing process using balls. When external electrodes are formed on the end surfaces of the laminated body, a large contact area with the internal electrodes can be obtained. Therefore, a reliability of the electrical connection between the electrodes is definitely secured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to multi layer ceramic electroniccomponents and methods for manufacturing the electronic components.Furthermore, the present invention relates to an improvement in thereliability of electrical connections between internal electrodes andexternal electrodes, which are provided in the multi layer ceramicelectronic components.

2. Description of the Related Art

Typical examples of multi layer ceramic electronic components inconnection with the present invention are laminate-type theorists havinga positive temperature coefficient. The laminate-type theorist having apositive temperature coefficient usually has the structure describedbelow.

The laminate-type theorist having a positive temperature coefficientincludes a laminated body as a main component. The laminated body has aplurality of ceramic layers and a plurality of internal electrodes thatextend along predetermined interfaces between the ceramic layers. Theceramic layers are composed of a theorist material having a positivetemperature coefficient of resistance. The internal electrodes includefirst internal electrodes that extend to a first end surface of thelaminated body and second internal electrodes that extend to a secondend surface, opposite the first end surface, of the laminated body. Thefirst electrodes and the second electrodes are alternately arranged inthe lamination direction.

The laminate-type theorist having a positive temperature coefficient isprovided with a first external electrode and a second external electrodewhich are disposed on the first and second end surfaces, respectively,of the laminated body. The first external electrode is in electricalcontact with the first internal electrodes at the first end surface ofthe laminated body. The second external electrode is in electricalcontact with the second internal electrodes at the second end surface ofthe laminated body.

Such a laminate-type theorist having a positive temperature coefficientis usually manufactured according to the method described below.

A step for preparing a green laminated body is conducted. The greenlaminated body is converted into the above-mentioned skittered laminatedbody by firing. The green laminated body includes ceramic green sheetsfor ceramic layers and conductive paste films for the internalelectrodes.

In particular, the ceramic green sheets are prepared by mixing a powderyceramic material such as a Batik₃-based material, an organic binder, andan organic solvent in order to make a slurry and by forming the slurryinto sheets by a doctor blade method or the like.

Conductive paste is prepared by mixing a base metal powder such as Inpowder, an organic binder, and an organic solvent. The conductive pasteis applied on the ceramic green sheets by a screen-printing method orthe like to provide conductive paste films for the internal electrodes.

The green laminated body is prepared by laminating the plurality ofceramic green sheets provided with the conductive paste films for theinternal electrodes, and by pressing the laminated ceramic green sheetsin the lamination direction.

The resulting green laminated body may be cut, if necessary, and then isskittered to provide a skittered laminated body. When a base metal suchas Ni is used as the conductive element for the internal electrodes, thesintering process is conducted under a reducing atmosphere in order toprevent oxidation of the base metal. In such a case, after the sinteringprocess, the skittered laminated body is heated (revalidation) under anoxidizing atmosphere to provide the ceramic layers with positivetemperature characteristics.

The skittered laminated body is then polished by barrel polishing thatis generally conducted for most of the chip-type ceramic electroniccomponents in a manufacturing process. The barrel polishing process isconducted to prevent chipping of the laminated body or to prevent achange in characteristic caused by chipped ceramic debris of thelaminated body adhering to another laminated body. The barrel polishingprocess rounds the corners and the edges of the skittered laminatedbody.

The external electrodes are formed by, for example, sputtering or firingthe conductive paste on the first end surface and the second end surfaceof the laminated body. The external electrodes are composed of a metalhaving high affinity with a metal that is contained in the internalelectrodes.

However, the laminate-type theorist having a positive temperaturecoefficient manufactured by the method described above may havefollowing problems.

In general, the conductive paste films have high contractibilitycompared with the ceramic green sheets. Therefore, when the greenlaminated body having the ceramic green sheets and the conductive pastefilms is monolithic ally fired in the sintering process, the internalelectrodes may not reach the end surfaces of the skittered laminatedbody. In such a case, the internal electrodes are not completelyconnected to the external electrodes electrically and mechanically. As aresult, the multi layer ceramic electronic component such as thelaminate-type theorist having a positive temperature coefficient cannotexhibit satisfactory characteristics.

A possible solution to this problem is disclosed in, for example,Japanese Unexamined Patent Application Publication No. 6-181101. In thismethod, a conductive paste for external electrodes is applied on endsurfaces of a green laminated body having ceramic green sheets and aconductive paste for internal electrodes before firing the greenlaminated body. Specifically, the ceramic green sheets, the conductivepaste for internal electrodes, and the conductive paste for externalelectrodes are fired at the same time.

According to this method, when the conductive paste for externalelectrodes is applied to the green laminated body, the shrinkage causedby firing the conductive paste for internal electrodes inside the greenlaminated body does not occur. Therefore, the conductive paste forexternal electrodes and the conductive paste for internal electrodescertainly come into contact with each other. As a result, electrical andmechanical connections between the external electrodes and the internalelectrodes are ensured.

However, this method has the following problem. In the above-mentionedmethod, the barrel polishing process for preventing chipping of theskittered laminated body must be conducted after the firing process.Specifically, when the sintering process is completed, the skitteredlaminated body is already provided with the external electrodes.Accordingly, the external electrodes are partially polished by barrelpolishing. As a result, the reliability of the electrical connectionbetween the external electrodes and the internal electrodes may bedecreased.

For example, Japanese Unexamined Patent Application Publication Nods.11-288840 and 11-288841 disclose a method for removing a particularportion, i.e. The ceramic layer, of the end surfaces of the skitteredlaminated body mechanically by sandblasting the end surfaces of theskittered laminated body. As a result, the end portions of the internalelectrodes are sufficiently exposed at the end surfaces of the laminatedbody.

However, when the above-mentioned method is applied to a laminated bodythat has high-hardness ceramic layers, for example, a laminated body fora multi layer ceramic capacitor, not only the ceramic layers are removedbut also the internal electrodes are undesirably removed. Accordingly,the sandblasting process may be meaningless and a reliable electricalconnection between the internal electrodes and external electrodes maynot be provided.

When the sandblasting is conducted, the end surfaces of the laminatedbodies must be aligned in the blowing direction of alumna powder or thelike. Accordingly, the sandblasting of a large number of laminatedbodies require many working hours for aligning the laminated bodies inthe desired direction. Therefore, sandblasting is unsuitable for massproduction.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a multi layer ceramic electroniccomponent which has improved reliability in terms of electrical andmechanical connections of internal electrodes and external electrodes,and a method of manufacturing such a novel multi layer ceramicelectronic component.

According to a preferred embodiment of the present invention, a multilayer ceramic electronic component includes a laminated body andexternal electrodes. The laminated body includes a plurality of ceramiclayers and a plurality of internal electrodes extending alongpredetermined interfaces between the ceramic layers. The externalelectrodes are disposed on the end surfaces extending in the laminationdirection of the laminated body and are in electrical contact with thepredetermined internal electrodes. The present invention can solve theabove-mentioned technological problems with the unique structuredescribed below.

More specifically, each of the internal electrodes includes a mainportion located between the ceramic layers, and an end portion extendingfrom the main portion and being in electrical contact with the externalelectrode on the end surface of the laminated body. The end portion ischaracterized by an extension along the end surface of the laminatedbody.

Such a structure allows the contact area between the internal electrodesand the external electrode to increase. Therefore, the reliability ofthe electrical contact between the internal electrodes and the externalelectrodes is increased and the strength of the connection between theinternal electrodes and the external electrodes is increased. As aresult, the resistance characteristics of the multi layer ceramicelectronic component can be stabilized.

When the internal electrodes for the multi layer ceramic electroniccomponent according to preferred embodiments of the present inventionhave a specific structure as described above, there are two possibletypes of extension. A first extension extends in one direction along theend surface of the laminated body so that the end portion and the mainportion of the internal electrode together define a substantiallyL-shaped cross-section. A second extension extends in differentdirections along the end surface of the composite so that the endportion and the main portion of the internal electrode together define asubstantially T-shaped cross-section.

The second extension of the two shapes is particularly preferablebecause the second extension can provide a larger contact area betweenthe internal electrodes and the external electrodes than the firstextension can. Therefore, the reliability of the electrical andmechanical connections between the internal electrodes and the externalelectrodes can be increased.

In particular, the present invention is advantageously applied to amulti layer ceramic electronic component having the following structure.The multi layer ceramic electronic component has external electrodes andinternal electrodes. The external electrodes include a first externalelectrode disposed on a first end surface of a laminated body and asecond external electrode disposed on a second end surface, opposite thefirst end surface, of the laminated body. The internal electrodesinclude first internal electrodes in electrical contact with the firstexternal electrode and second internal electrodes in electrical contactwith the second external electrode. The first internal electrodes andthe second internal electrodes are alternately disposed in thelamination direction of the laminated body. Examples of the multi layerceramic electronic component having such a structure include alaminate-type theorist having a positive temperature coefficient, alaminate-type theorist having a negative temperature coefficient, alaminate-type ceramic capacitor, and a laminate-type ceramic varsity.

The present invention can be advantageously applied to a multi layerceramic electronic component including the ceramic layers composed of asemi conductive ceramic having a positive temperature coefficient ofresistance, for example, a laminate-type theorist having a positivetemperature coefficient. When the specific structure according to apreferred embodiment of the present invention is applied to thelaminate-type theorist having a positive temperature coefficient, theresistance of the electrical contact area between the internalelectrodes and the external electrodes can be decreased and theconnection between the internal electrodes and the external electrodescan be stabilized. Therefore, the resistance value is stabilized and thetheorist characteristics such as Curie temperature can be stabilized.Stability in an overload test can also be secured.

In the multi layer ceramic electronic component according to a preferredembodiment of the present invention, preferably, the ceramic layers havea skittered density between about 60% and about 85% and the mainportions of the internal electrodes have a thickness of about 0.5 μm ormore. With such a structure, when the multi layer ceramic electroniccomponent is manufactured by processes as described-below, the endportions can have the extensions extending along the end surfaces of thelaminated body. The main portion of the internal electrode having athickness of about 3.0 μm or less can further decrease the desalinationbetween the ceramic layers and the internal electrodes.

Another preferred embodiment of the present invention provides a methodfor manufacturing the multi layer ceramic electronic component includinga laminated body and external electrodes. The laminated body includes aplurality of ceramic layers and a plurality of internal electrodesextending along predetermined interfaces between the ceramic layers. Theexternal electrodes are disposed on end surfaces extending in thelamination direction of the laminated body and are in electrical contactwith the predetermined internal electrodes.

The method for manufacturing the multi layer ceramic electroniccomponent according to a preferred embodiment of the present inventionincludes the steps of preparing a green laminated body, sintering thegreen laminated body into a skittered laminated body, and formingexternal electrodes on the end surfaces of the skittered laminated body.The green laminated body includes ceramic green sheets for the ceramiclayers and conductive paste films for the internal electrodes.

For solving the above-mentioned technological problems during such amanufacturing process, preferred embodiments of the present inventionhave the following unique characteristics.

In the step of preparing the green laminated body, the thickness of theconductive paste films is determined so that the internal electrodesafter the step of sintering preferably have a thickness between about0.5 μm and about 3.0 μm. Furthermore, the step of sintering iscontrolled so that the ceramic layers of the skittered laminated bodyhave a skittered density between about 60% and about 85%.

A barrel polishing process is conducted between the steps of sinteringand the steps of forming the external electrodes. By barrel polishingthe skittered laminated body with balls, the end portions of theinternal electrodes protrude from the end surfaces of the skitteredlaminated body and then are deformed to extend along the end surfaces.The protruding and deforming end portions of the internal electrodescome into electrical contact with the external electrodes.

In the method for manufacturing the multi layer ceramic electroniccomponent, extensions which extend along the end surfaces of thelaminated body can be efficiently formed at the end portions of theinternal electrodes by the barrel polishing process.

More specifically, the internal electrodes preferably have a thicknessof about 0.5 μm or more so as to keep a predetermined strength. Theceramic layers preferably have a low skittered density such as about 85%or less. With this combination, the strength of the ceramic layers canbe reduced so as to be lower than that of the internal electrodes in theskittered laminated body. Under the circumstances, the ceramic layersare chipped off earlier than the internal electrodes by the barrelpolishing process using the balls for the skittered laminated body.Therefore, the end portions of the internal electrodes protrude from theend surfaces of the laminated body. The protruding end portions of theinternal electrodes are struck toward the end surfaces of the laminatedbody by the balls. As a result, the end portions are caused to extendalong the end surfaces of the laminated body and then are flattened byplastic deformation. Consequently, the end portions, which function asthe area of contact with the external electrodes, of the internalelectrodes define extensions extending on the end surfaces of thelaminated body.

In the method for manufacturing the multi layer ceramic electrodecomponent according to a preferred embodiment of the present invention,preferably, the balls have a diameter smaller than the dimension of theend surfaces of the laminated body in the lamination direction. If thediameter of the balls is larger than the dimension of the end surfacesof the laminated body in the lamination direction, the end portions,protruding from the end surfaces of the laminated body, of the internalelectrodes are easily chipped off.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a multi layer ceramicelectronic component according to a preferred embodiment of the presentinvention.

FIG. 2 is an enlarged cross-sectional view illustrating an end surfaceof a skittered laminated body after a sintering process for preparingthe multi layer ceramic electronic component shown in FIG. 1.

FIG. 3 is a view, corresponding to FIG. 2, illustrating internalelectrodes protruding from the end surface of the laminated body in abarrel polishing process that the skittered laminated body shown in FIG.2 is subjected to.

FIG. 4 is a view, corresponding to FIG. 2, illustrating deformed endportions of the internal electrodes, which are substantiallyconcurrently formed with the protrusion shown in FIG. 3, in the barrelpolishing process.

FIG. 5 is a view, corresponding to FIG. 2, illustrating an externalelectrode that is formed after the deformation shown in FIG. 4.

FIG. 6 is a view, corresponding to FIG. 2, illustrating an end surfaceof the skittered laminated body when the barrel polishing process wasinadequately conducted, as a description of a comparative example.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A structure of a multi layer ceramic electronic component 1 shown inFIG. 1 is applicable to, for example, a laminate-type theorist having apositive temperature coefficient, a laminate-type theorist having anegative temperature coefficient, a laminate-type ceramic capacitor, anda laminate-type ceramic varsity.

With reference to FIG. 1, the multi layer ceramic electronic component 1includes a laminated body 2 as a main part of the component. Thelaminated body 2 includes a plurality of ceramic layers 3 and aplurality of internal electrodes 4 and 5 extending along predeterminedinterfaces between the ceramic layers 3. The internal electrodes 4 and 5include first internal electrodes 4 which extend to a first end surface6 of the laminated body 2 and second internal electrodes 5 which extendto a second end surface 7, opposite the first end surface 6 of thelaminated body 2. The first and second end surfaces 6 and 7 extend inthe lamination direction of the laminated body 2. The first electrodes 4and the second electrodes 5 are alternately arranged in the laminationdirection of the laminated body 2.

A ceramic material for the ceramic layers 3 is determined depending onthe function of the multi layer ceramic electronic component 1. Inparticular, the ceramic layers 3 may be composed of, for example, semiconductive ceramics, dielectric ceramics, piezoelectric ceramics, ormagnetic ceramics. When the multi layer ceramic electronic component 1is a laminate-type theorist having a positive temperature coefficient,the ceramic layers 3 are preferably composed of a theorist materialhaving a positive temperature coefficient of resistance, i.e. The semiconductive ceramics. Examples of the semiconductive ceramics includebarium titrate ceramics. When the multi layer ceramic electroniccomponent 1 is a laminate-type ceramic capacitor, the ceramic layers 3are composed of dielectric ceramics.

Examples of a conductive component which is contained in the firstinternal electrodes 4 and the second internal electrodes 5 include basemetals such as In and Cu, noble metals such as Ag, Pd, and Pt, andalloys of these metals. In particular, when the multi layer ceramicelectronic component 1 is a laminate-type theorist having a positivetemperature coefficient, the first internal electrodes 4 and the secondinternal electrodes 5 are composed of a metal, such as Ni, which are inan ohmic contact with the ceramic layers 3.

The multi layer ceramic electronic component 1 includes a first externalelectrode 8 and a second external electrode 9 which function asterminals. The first external electrode 8 and the second externalelectrode 9 are disposed on the first end surface 6 and the second endsurface 7, respectively, of the laminated body 2. The first externalelectrode 8 is electrically connected with the first internal electrodes4 on the first end surface 6 of the laminated body 2. The secondexternal electrode 9 is electrically connected with the second internalelectrodes 5 on the second end surface 7 of the laminated body 2.

The first and second external electrodes 8 and 9 are formed by, forexample, sputtering, or other suitable process. Specifically, each ofthe first and second external electrodes 8 and 9 preferably includes aNi—Cr layer 10, a Cu layer 11 on the Ni—Cr layer 10, and an Ag layer 12on the Cu layer 11. The Ni—Cr layer 10 and the Cu layer 11 can bereplaced with, for example, a Cr layer or a Ni layer. The Ag layer 12enhances the plating deposition strength and solderability of thesurfaces of the first and second external electrodes 8 and 9. Ag in thelayer 12 may be replaced with a metal other than Ag.

The first and second external electrodes 8 and 9 may be formed byapplying a conductive paste on the first and second end surfaces 6 and 7of the laminated body 2 and then firing. The conductive paste ispreferably prepared by dispersing a conductive metal powder and anorganic binder into an organic solvent. When the firing process isconducted under an oxidizing atmosphere such as air, the conductivemetal powder contained in the conductive paste is composed of a noblemetal such as Ag, Pd, or Pt, which is barely oxidized. When the firingprocess is conducted under a non-oxidizing atmosphere, the conductivemetal powder may be composed of a base metal such as Cu and Ni.

A first plating layer 13 and a second plating layer 14 are disposed onthe first external electrode 8 and the second external electrode 9,respectively, if necessary. The first and second plating layers 13 and14 enhance the solderability and prevent the Ag layers 12 of the firstand second external electrodes 8 and 9 from being lost by soldering. Themetal for the first and second plating layers 13 and 14 is determineddepending on the affinity with the metal contained in the surface layersof the first and second external electrodes 8 and 9. When the surfacelayers of the first and second external electrodes 8 and 9 are the Aglayers 12, each of the first and second plating layers 13 and 14 iscomposed of a Ni sublayer 15 and a Sn sublayer 16 disposed on the Nisublayer 15. The Sn sublayer 16 may be replaced with a solder layer.

A protective coating (not shown in FIG. 1) composed of, for example,glass, may be partially disposed on exposed surfaces of the laminatedbody 2, the first and second external electrodes 8 and 9 not beingdisposed on the exposed surfaces. The protective coat protects thelaminated body 2 from the external environment, i.e. externaltemperature, moisture, and the like which deteriorate thecharacteristics of the multi layer ceramic electronic component 1. Whenthe laminated body 2 is provided with the ceramic layers 3 composed ofsemi conductive ceramic, undesirable plating of the exposed surfaces ofthe laminated body 2 and penetration of the plating solution into thelaminated body 2 may be caused during the formation of the first andsecond plating layers 13 and 14 on the first and second externalelectrodes 8 and 9. The protective coat can prevent such deteriorationin characteristics.

FIG. 5 illustrates a structure including some of the uniquecharacteristics of a preferred embodiment of the present invention. FIG.5 shows a side where the second end surface 7 of the laminated body 2resides. The configuration of the first end surface 6 is preferablysubstantially the same.

With reference to FIG. 5, each of the first and second internalelectrodes 4 and 5 includes a main part 17 disposed between the ceramiclayers 3, and an end portion 18 connecting to the main part 17 and beingin electrical contact with the corresponding first or second externalelectrode 8 or 9 at the respective end surface 6 or 7 of the laminatedbody 2. The end portion 18 has an extension extending along thecorresponding end surface 6 or 7 of the laminated body 2.

Typically, the end portion 18 and the main part 17 define asubstantially T-shaped cross-section 19 shown in the upper portion ofFIG. 5 or define a substantially L-shaped cross-section 20 shown incentral and lower portions of FIG. 5. The end portion 18 having thesubstantially T-shaped cross-section 19 has an extension extending fromthe main part 17 in different directions on the corresponding endsurface 6 or 7 of the laminated body 2. The end portion 18 having theL-shaped cross-section 20 has an extension extending from the main part17 to one direction on the corresponding end surface 6 or 7 of thelaminated body 2.

The substantially T-shaped cross-section 19 and the substantiallyL-shaped cross-section 20 shown in the drawing are typical examples.Practically, the end portions 18 having intermediate shapes of them maybe formed. The end portions 18, having the substantially T-shapedcross-section 19 and the substantially L-shaped cross-section 20, of theinternal electrode 4 or 5 also may be provided in combination on one endsurface.

The above-mentioned structure enlarges the contact area between each ofthe first and second internal electrodes 4 and 5 and each of the firstand second external electrodes 8 and 9. Therefore, the reliability ofelectrical conduction and the mechanical connection are greatly improvedbetween the first and second internal electrodes 4 and 5 and the firstand second external electrodes 8 and 9. Especially, the reliability ofthe electrical conduction and the strength of the mechanical connectioncan be highly enhanced by the substantially T-shaped end portion 18 ofthe first and second internal electrodes 4 and 5 compared with thesubstantially L-shaped end portion 18.

Such specific shapes of the end portions 18 of the first and the secondinternal electrodes 4 and 5 can be prepared, while providing differentstrengths between the ceramic layers 3 and the internal electrodes 4 and5, by the following method for manufacturing a multi layer ceramicelectronic component described below.

A green laminated body including ceramic green sheets for ceramic layers3 and conductive paste films for the first and the second internalelectrodes 4 and 5 is prepared. The green laminated body is thenskittered to provide the skittered laminated body 2. FIG. 2 is a partialenlarged view of the second end surface 7 of the resulting laminatedbody 2 after the sintering process.

In the process for preparing the green laminated body, the thickness ofthe conductive paste is determined such that each of the first and thesecond internal electrodes 4 and 5 formed by the sintering process has athickness of at least about 0.5 μm. In the sintering process, theskittered laminated body 2 is provided with ceramic layers 3 having askittered density of between about 60% and about 85%. The skittereddensity refers to a relative ratio to a theoretical density calculatedfrom the ceramic composition of the ceramic layers 3.

A barrel polishing process is performed on the skittered laminated body2. The barrel polishing process is conducted in the presence of balls.FIGS. 3 and 4 show a typical resultant state, after the barrel polishingprocess, of the same portion as that shown in FIG. 2.

Each of the first and second internal electrodes 4 and 5 preferably hasa thickness of at least about 0.5 μm and has a strength exceeding apredetermined strength. Each of the ceramic layers 3 preferably has askittered density of lower than about 85% so that the strength of theceramic layers 3 is lower than that of the first and second internalelectrodes 4 and 5 in the skittered laminated body 2. Under suchconditions, as shown in FIG. 3, the ceramic layers 3 are chipped offduring barrel polishing before the first and second internal electrodes4 and 5 are chipped off. As a result, the end portions 18 of the firstand second internal electrodes 4 and 5 protrude from the first andsecond end surfaces 6 and 7 of the laminated body 2. FIG. 3 illustratesthe second end surface 7 of the laminated body 2 and a broken line showsa position of the second end surface 7 in the state before the barrelpolishing process.

While the ceramic layers 3 are chipped off, the balls strike the endportions 18 protruding from the first and second internal electrodes 4and 5 toward the first and second end surfaces 6 and 7 of the laminatedbody 2. As a result, as shown in FIG. 4, the end portions 18 of thefirst and second internal electrodes 4 and 5 are bent on the first andsecond end surfaces 6 and 7 so that the end portions 18 extend along theend surfaces 6 and 7 and are expanded by plastic deformation. Thus, theend portions 18 of the first and second internal electrodes 4 and 5 areshaped into the substantially T-shaped cross-section 19 or thesubstantially L-shaped cross-section 20.

When the thickness of the first and second internal electrodes 4 and 5is less than about 0.5 μm, the end portions 18 of the first and secondinternal electrodes 4 and 5 are easily removed together with the ceramiclayers 3 by barrel polishing using the balls even if the end portions 18of the internal electrodes 4 and 5 protrude at one time from the firstand second end surfaces 6 and 7 of the laminated body 2.

When the thickness of the first and second internal electrodes 4 and 5is larger than about 3.0 μm, desalination tends to occur during firingthe green laminated body. Consequently, the resistivity of the multilayer ceramic electronic component 1 tends to increase.

When the skittered density of the ceramic layers 3 is larger than about85%, the removal of the ceramic layers 3 by barrel polishing thelaminated body 2 is insufficient for the end portions 18 of the firstand second internal electrodes 4 and 5 to protrude. Therefore, it isdifficult to form the end portions 18 of the first and second internalelectrodes 4 and 5 into the substantially T-shaped cross-section 19 andthe substantially L-shaped cross-section 20.

The ceramic layers 3 preferably have a skittered density of at leastabout 60%. When the ceramic layers 3 have a skittered density of lessthan about 60%, the strength of the ceramic layers 3 is insufficient. Asa result, the ceramic layers 3 cannot exhibit sufficient mechanicalstrength for practical use as a component of the laminated body 2.

By adequately selecting the type and content of the metal powder in theconductive paste for the first and second electrodes 4 and 5, the firstand second internal electrodes 4 and 5 can exhibit a higher strengththan that of a predetermined strength. However, as described in thispreferred embodiment, a thickness of at least about 0.5 μm can readilyenhance the strength of the first and second internal electrodes 4 and5. This is a valuable, yet simple method.

By increasing the organic binder content in the ceramic green sheets forthe ceramic layers 3, or by decreasing the sintering temperature used toprepare the skittered laminated body 2, the skittered density can bereduced in order to decrease the strength of the ceramic layers 3.

Preferably, the diameter of the balls used in the barrel polishingprocess is smaller than the dimension of the first and second endsurfaces 6 and 7 of the laminated body 2 in the lamination direction.Even if the end portions 18 of the first and second electrodes 4 and 5have once protruded from the first and second end surfaces 6 and 7 ofthe laminated body 2, balls having a diameter larger than the dimensionof the first and second end surfaces 6 and 7 of the laminated body 2readily chip off the protruding end portions 18.

Any balls can be used for the barrel polishing process. Examples of theballs include Si-based, Al-based, and Zr-based materials. In the barrelpolishing process, water, an abrasive powder such as SiO₂ and Al₂O₃, andother additive, in addition to the balls, may be used.

Barrel polishing conditions, i.e., the ratio of the balls, the laminatedbody 2, water, the abrasive powder, and the additive and the rotatingspeed and the time for the barrel polishing process determine which ofthe substantially T-shaped cross-section 19 and the substantiallyL-shaped cross-section 20 is mainly formed.

As shown in FIGS. 1 and 5, the first and second external electrodes 8and 9 are disposed on the respective first and second end surfaces 6 and7 of the laminated body 2. If necessary, first and second plating layers13 and 14 and a protective coating (not shown) preferably composed ofglass or other suitable material are formed to complete the multi layerceramic electronic component 1.

Preferred embodiments of the present invention will now be explainedwith reference to Examples. In the Examples, laminate-type theoristshaving a positive temperature coefficient are manufactured as samples.

EXAMPLE 1

Powders of BaCo₃, TiO₂, and Sm₂O₃ were prepared. These powders weremixed so as to form a composition of (Ba_(0.998) Sm_(0.002))TiO₃.

Deionized water was added to the mixed powder and then the mixture wascrushed by stirring with zirconia balls for 10 hours. After drying themixture, the obtained powder was calcinated at 1,000° C. for 2 hours andthen pulverized to prepare a calcinated powder.

An organic binder, a dispersant, and water were added to the calcinatedpowder and these were mixed with zirconium balls for several hours toprepare a ceramic slurry. To prepare a plurality of types of ceramiclayers having different skittered densities between about 50% and about90% after a sintering process (described later), ceramic slurries havingvarious amount of organic binder were prepared. The skittered densitiesafter sintering are shown in the column “skittered density” of Table 1.

Each of the ceramic slurries was formed into sheets by a doctor blademethod and then dried to prepare ceramic green sheets.

A conductive paste composed of Ni powder, an organic binder, and anorganic solvent were prepared. The conductive paste was applied on theceramic green sheet by screen-printing to form a conductive paste filmfor an internal electrode. To provide a plurality of types of internalelectrodes each having a thickness between about 0.3 μm and about 3.6 μmafter a sintering process (described later), a plurality of types ofconductive paste films having different thicknesses were prepared. Thethicknesses after sintering are shown in the column “internal electrodethickness” of Table 1.

These ceramic green sheets were laminated so that the conductive pastefilms oppose each other with the ceramic green sheets disposedtherebetween. The ceramic green sheets which were not provided with theconductive paste were disposed on the bottom and the top of thelaminated ceramic green sheets. The resulting laminated ceramic greensheets were press-bonded and then cut into green laminated bodies havingapproximate dimensions of a length of 2.2 mm, a width of 2.75 mm, and athickness of 1.2 mm, for example.

Each green laminated body was degreased in air at 400° C. for 2 hoursand then skittered in a H₂(3%)—N₂ reducing atmosphere at 1,300° C. for 2hours. The sintering process converted the ceramic green layers and theconductive paste films into ceramic layers and internal electrodes,respectively, and provided a skittered laminated body.

The skittered laminated bodies were mixed with balls which were composedof Si and Al and which had a diameter of about 1 mm. A predeterminedamount of water was added to the mixture with the skittered bodies andthen a barrel polishing process was conducted.

The resulting laminated bodies after barrel polishing were reoxidized inair at 700° C.

External electrodes were formed on both end surfaces of the laminatedbody by depositing a Ni—Cr layer, Cu layer, and then Ag layer bysputtering. Furthermore, plating layers were formed on the externalelectrodes by depositing Ni sublayers and then Sn sublayers byelectroplating.

As described above, laminate-type theorists having a positivetemperature coefficient used as samples were prepared. Theselaminate-type theorists having a positive temperature coefficient wereevaluated for the following characteristics:

1. Resistance Value at Room Temperature

Twenty laminate-type theorists having a positive temperature coefficientfor samples of each type were prepared. The resistance at roomtemperature (25° C.) was measured for each of the laminate-typetheorists having a positive temperature coefficient. The average,maximum, minimum, and standard deviation (σ) of resistance of samples ofsame type were determined. The resistance at room temperature is anindicator of the stability of the connection between the internalelectrodes and the external electrodes.

2. Transverse Strength

Ten laminate-type theorists having a positive temperature coefficientfor samples of each type were prepared. The transverse strengths weremeasured for each sample according to JIS C 5102 “Section 8.12 Strengthof capacitor body” in “Testing procedure of fixed capacitor forelectronic devices” and the average was calculated. The transversestrength is an indicator of the mechanical strength of the laminatedbody, i.e. of the laminate-type theorist having a positive temperaturecoefficient.

3. Incidence Rate of Desalination

Fifty laminate-type theorists having a positive temperature coefficientfor samples of each type were prepared. Each laminate-type theoristhaving a positive temperature coefficient was cut from one externalelectrode to the other external electrode in parallel to the laminationdirection. The resulting longitudinal section was polished and thenvisually inspected. The probability of desalination was determined as apercentage of the number of delaminated samples to the number of totalsamples.

The resistance at room temperature, transverse strengths, and incidencerate of desalination are shown in Table 1 below.

TABLE 1 Internal incidence Sintered Electrode transverse rate of DensityThickness Resistance at Room Temperature (Ω) Strength DelaminationSample (%) (μm) Average Maximum Minimum σ (N) (%) *1  50 1.5 0.348 0.410.31 0.03 21 0 2 60 1.5 0.345 0.38 0.32 0.015 46 0 3 70 1.5 0.311 0.340.29 0.016 49 0 4 80 1.5 0.309 0.33 0.28 0.013 52 0 *5  85 0.3 0.8691.24 0.56 0.175 54 0 *6  85 0.4 0.59 0.82 0.34 0.154 47 0 7 85 0.5 0.3270.37 0.27 0.03 56 0 8 85 1 0.316 0.36 0.29 0.017 51 0 9 85 1.5 0.3150.34 0.29 0.014 53 0 10  85 2 0.305 0.34 0.29 0.011 53 0 11  85 2.50.299 0.32 0.29 0.009 53 0 12  85 3 0.306 0.33 0.28 0.013 54 0 *13  853.3 0.306 0.33 0.29 0.012 51 4 *14  85 3.6 0.301 0.33 0.28 0.011 55 22 *15  90 1.5 0.492 0.71 0.34 0.108 58 0

In Table 1, samples with an asterisk * were manufactured under differentconditions from the manufacturing conditions according to variouspreferred embodiments of the present invention.

As shown in Table 1, all samples having an “internal electrodethickness” of at least about 0.5 μm and a “skittered density” betweenabout 60% and about 85%, i.e. Samples 2 to 4 and 7 to 14 exhibited a lowresistance at room temperature, that is to say, the “averages” of the“resistance at room temperature” were about 0.35Ω or less.

Especially, among the above-mentioned samples, samples having an“internal electrode thickness” of about 3.0 μm or less, i.e., Samples 2to 4 and 7 to 12 did not have desalination, that is to say, “incidencerate of desalination” were 0%. The longitudinal sections of thelaminate-type theorists having a positive temperature coefficient ofSamples 2 to 4 and 7 to 12 were inspected. With reference to FIG. 5,each of the end portions 18 of the first and second internal electrodes4 and 5 had an extension extending along the respective first and secondend surfaces 6 and 7 of the laminated body 2. More specifically, the endportion 18 had a substantially T-shaped cross-section 19 or asubstantially L-shaped cross-section 20.

On the other hand, Samples 5 and 6 having an “internal electrodethickness” of less than about 0.5 μm exhibited a high resistance at roomtemperature, that is to say, the “averages” of the “resistance at roomtemperature” were about 0.5Ω or more. The “σ” values were significantlyhigh. This is because that the electrical connection between theinternal electrodes and the external electrodes was insufficient.

Sample 1, of which “skittered density” was less than about 60%,exhibited a significantly low “transverse strength” compared with thoseof other samples. This suggests that the laminate-type theorist having apositive temperature coefficient having a “skittered density” of lessthan about 60% has insufficient mechanical strength and that such alaminate-type theorist having a positive temperature coefficient may bedamaged in practical use as well as in the mounting process.

Sample 15, of which “skittered density” was higher than about 85%,exhibited a high “average” of “resistance at room temperature”, i.e.,higher than about 0.45Ω. The longitudinal section surfaces of thelaminate-type theorists having a positive temperature coefficient ofsample 15 were visually inspected. With reference to FIG. 6, the endportions 18 of the first and second internal electrodes 4 and 5 did notprotrude from the first and second end surfaces 6 and 7 of the laminatedbody 2. This means that the electrical connections between the first andsecond internal electrodes 4 and 5 and the first and second externalelectrodes 8 and 9, respectively, were insufficient. In FIG. 6, the sameelements are indicated by the same reference numerals as in FIG. 5.

EXAMPLE 2

In order to determine the influence of the shape of the end portion ofthe internal electrodes on the stability of resistance of thelaminate-type theorist having a positive temperature coefficient, Sample9 in EXAMPLE 1 was used as a standard for comparison and laminate-typetheorists having a positive temperature coefficient of Samples 16 and 17were prepared. Samples 16 and 17 had different shaped end portions ofthe internal electrodes from that of Sample 9.

Specifically, the laminated body of the laminate-type theorists having apositive temperature coefficient for Samples 16 and 17 were the same asthat of Sample 9. A barrel polishing process for Sample 16 was conductedby using balls having a diameter of about 5 mm, which is larger than thedimension of the end surfaces of the laminated body in the laminationdirection. The end portions of the internal electrodes were conducted bysandblasting the end surfaces of the laminated body. A barrel polishingprocess for Sample 17 was conducted by using the same balls as those ofSample 9, but the amount of the balls was less than that of Sample 9. Asa result, the end portions of the internal electrodes were formed into asubstantially L-shaped cross-section more than a substantially T-shapedcross-section.

After the sandblasting process, the laminate-type theorists having apositive temperature coefficient of Samples 16 and 17 were prepared bythe same manufacturing processes as those of Sample 9.

Resistance at room temperature of the resulting laminate-type theoristshaving a positive temperature coefficient of Samples 16 and 17 weredetermined by the same method as that used in EXAMPLE 1. The average,maximum, minimum, and standard deviation (a) of resistances of samplesare shown in Table 2. Table 2 includes the “resistance at roomtemperature” of Sample 9 shown in Table 1 for easier comparison.

In order to evaluate the reliability, i.e. The stability of resistance,of each of the laminate-type theorists having a positive temperaturecoefficient of Samples 9, 16, and 17, an intermittent energizing testwas carried out. Ten laminate-type theorists having a positivetemperature coefficient for samples of each type were prepared. Each ofthe laminate-type theorists having a positive temperature coefficientwas energized with a voltage of 6 V for 30 seconds and with one-minuteinterruption as one cycle. After 1,000 cycles were repeated as theintermittent energizing test, the resistance at room temperature wasdetermined. The rate of change of the resistance at room temperaturefrom after to before the intermittent energizing test was determined.The average is shown in column “Rate of change of resistance” of Table2.

TABLE 2 Rate of Change Resistance at Room Temperature (Ω) in ResistanceSample Average Maximum Minimum σ (%)  9 0.315 0.34 0.29 0.014 1.8 160.319 0.34 0.31 0.011 9.6 17 0.309 0.33 0.3 0.008 4.7

As shown in Table 2, before the loading by the intermittent energizingtest, Samples 16 and 17 exhibited similar resistances at roomtemperature to those of Sample 9. Expansion and contraction stress bythermal cycles such as the intermittent energizing test increased theresistance. The rate of change of resistance in Sample 16 was themaximum, and then Sample 16 and Sample 9 followed. These results showthat a large end portion area, in contact with the external electrode,of the internal electrode decreased the rate of change of resistance andincreased the reliability of the connection.

A method for manufacturing a multi layer ceramic electronic componentaccording to various preferred embodiments of the present invention isadvantageous in manufacturing, for example, a laminate-type theoristhaving a positive temperature coefficient that particularly shows lowresistance and high stability at the connection between internalelectrodes and external electrodes.

The present invention is not limited to each of the above-describedpreferred embodiments, and various modifications are possible within therange described in the claims. An embodiment obtained by appropriatelycombining technical means disclosed in each of the different preferredembodiments is included in the technical scope of the present invention.

1. A multilayer ceramic electronic component comprising: a laminatedbody including a plurality of ceramic layers and a plurality of internalelectrodes extending along predetermined interfaces between the ceramiclayers and arranged on each other in a lamination direction; andexternal electrodes disposed on end surfaces extending in the laminationdirection of the laminated body, the external electrodes being inelectrical contact with the predetermined internal electrodes; whereineach of the internal electrodes includes a main portion located betweenthe ceramic layers and an end portion extending from the main portionand being in electrical contact with the external electrode on the endsurface of the laminated body, the end portion being an extensionextending along and in direct contact with the end surface laminatedbody; wherein the ceramic layers have a sintered density between about60% and about 85% and the main portions of the internal electrodes havea thickness of about 0.5 μm or more.
 2. The multilayer ceramicelectronic component according to claim 1, wherein the end portion isthe extension extending from the main portion in different directions onthe end surface of the laminated body so that the end portion and themain portion together define a substantially T-shaped cross-section. 3.The multilayer ceramic electronic component according to claim 1,wherein the end portion is the extension extending from the main portionin different directions on the end surface of the laminated body so thatthe end portion and the main portion together define a substantiallyL-shaped cross-section.
 4. The multilayer ceramic electronic componentaccording to claim 1, wherein the external electrodes include a firstexternal electrode disposed on a first end surface of the laminated bodyand a second external electrode disposed on a second end surface,opposite to the first end surface, of the laminated body, the internalelectrodes include a first internal electrode in electrical contact withthe first external electrode and a second internal electrode inelectrical contact with the second external electrode, and the firstinternal electrode and the second internal electrode are alternatelydisposed in the lamination direction.
 5. The multilayer ceramicelectronic component according to claim 1, wherein the ceramic layersare composed of a semi conductive ceramic having a positive temperaturecoefficient of resistance.
 6. The multilayer ceramic electroniccomponent according to claim 1, wherein the main portions of theinternal electrodes have a thickness of about 3.0 μm or less.